http://www.hobbytool.com/index.asp?P...WPROD&ProdID=4 these clamps that minnflyer suggested are the best, they are strong enough, but usually wont dent up the wood too much the metal ones with the rubber tips are really too strong for balsa and tend to crush the wood, there great for light ply though,they have alot of holding power.

also "T" pins a couple different sizes the pin insreter also comes in handy for the hard to stick surfaces.
as well as a small tap set for threading screws into just about anything,alot of builds require you to tap hardwood blocks and then harden the threads with thin CA,mostly wing mounts requiring a 1/4-20 tap for the nylon bolts to screw into but a small set is handy for engine mounting bolts also( I tap mine into the engine mount and also use a nut on the bottom to secure the bolts they will stay tight when there tapped in)most tap sets will come with the proper size drill bits for the taps if not then they will have a list of the right sizes its important to use the proper drill bit when making threads in any material